Helicene, hetero

Nitrogen and oxygen heteroatoms can also be introduced into helicenes. 5,10-Dihydrocarbazolo[3,4-c]carbazole 119 was the first helicene synthesized (in 1927). Heterohelicenes containing several nitrogen atoms as well as hydrogenated hetero-helicenes have been synthesized by Teuber and Vogel These authors also studied the consequences of the presence of sp centers in helicenes... 

Dehydrohelicenes are compounds in which both terminal aromatic rings of a (hetero-)helicene are connected through a a-bond... 

Since the first synthesis of PHelix Hgand 6, independently reported in 1997 by Bmnner and coworkers and by Reetz and coworkers, several [fij-helicene or hetero-[ ]-helicene scaffolds with appended phosphine functions have been built by using the classical oxidative photocyclization... 

Thiophen Analogues of Helicenes.— The photocyclization with iodine as oxidant of 1,2-di(diheteroaryl)ethenes, in which the heteroaryl group is derived from benzo[fe]thienyl or from tricyclic systems such as (434) or (440), is the key step in the synthesis of heterohelicenes. The ethylenes in turn are prepared from the aldehydes and the chloromethyl derivatives via phos-phonium salts or phosphonates through the Wittig reaction. The Bestmann method was also used for the synthesis of symmetrically substituted ethylenes from phosphonium periodates. Thus from (443) the heterohexahelicene (444) was obtained, (445) gave (446), and the hetero-heptahelicene (448) was obtained from (447). The undecahelicene (450) was prepared from (449). - These syntheses illustrate the fact that heterohelicenes are more easily available than helicenes, as the necessary aldehyde is prepared by metalation of (448) with butyl-lithium followed by reaction with iV-methylformanilide. The heptahelicene (452) was obtained by a double photocyclization of (451). 

Thiophen Analogues of Helicenes.— The reaction of seven heterohelicenes with AICI3 has been described. The products were compounds in which the two helical termini of a helicene are connected by a or-bond. The intramolecular ring-closure was limited to hetero-[5]- and -[6]-helicenes. A series of regularly annelated thiaheterohelicenes has been prepared by a new progressive annelation technique based on the key intermediate 2-methylbenzo[l,2-6 4,3-6 ]dithiophen. Two methano-bridged heterohelicenes have been prepared. The synthesis of some... 

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